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Magnetospheric Ion Influence on Magnetic Reconnection at the Duskside Magnetopause S

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Magnetospheric Ion Influence on Magnetic Reconnection at the Duskside Magnetopause S Faculty Scholarship 1-1-2016 Magnetospheric Ion Influence On Magnetic Reconnection At The Duskside Magnetopause S. A. Fuselier J. L. Burch P. A. Cassak J. Goldstein Follow this and additional works at: https://researchrepository.wvu.edu/faculty_publications Digital Commons Citation Fuselier, S. A.; Burch, J. L.; Cassak, P. A.; and Goldstein, J., "Magnetospheric Ion Influence On Magnetic Reconnection At The Duskside Magnetopause" (2016). Faculty Scholarship. 954. https://researchrepository.wvu.edu/faculty_publications/954 This Article is brought to you for free and open access by The Research Repository @ WVU. It has been accepted for inclusion in Faculty Scholarship by an authorized administrator of The Research Repository @ WVU. For more information, please contact [email protected]. PUBLICATIONS Geophysical Research Letters RESEARCH LETTER Magnetospheric ion influence on magnetic reconnection 10.1002/2015GL067358 at the duskside magnetopause Special Section: S. A. Fuselier1,2, J. L. Burch1, P. A. Cassak3, J. Goldstein1,2, R. G. Gomez1, K. Goodrich4, W. S. Lewis1, First Results from NASA's D. Malaspina4, J. Mukherjee1, R. Nakamura5, S. M. Petrinec6, C. T. Russell7, R. J. Strangeway7, Magnetospheric Multiscale 1,8 4 1,2 (MMS) Mission R. B. Torbert , K. J. Trattner , and P. Valek 1Southwest Research Institute, San Antonio, Texas, USA, 2University of Texas at San Antonio, San Antonio, Texas, USA, Key Points: 3Department of Physics and Astronomy, West Virginia University, Morgantown, West Virginia, USA, 4Laboratory for • Magnetospheric ions have significant Atmospheric and Space Physics, University of Colorado Boulder, Boulder, Colorado, USA, 5Space Research Institute, Austrian density at the magnetopause Academy of Sciences, Graz, Austria, 6Lockheed Martin Advanced Technology Center, Palo Alto, California, USA, 7Institute of • Magnetospheric ions do not influence 8 reconnection significantly at the Geophysics and Planetary Physics, University of California, Los Angeles, California, USA, Space Science Center and duskside magnetopause Department of Physics, University of New Hampshire, Durham, New Hampshire, USA Abstract Magnetospheric ions from the ring current, warm plasma cloak, and the plasmaspheric drainage Correspondence to: plume all interact with the dusk flank magnetopause. During periods of strong magnetospheric convection, S. A. Fuselier, fi [email protected] these ions may contribute signi cantly to the magnetospheric mass density at the magnetopause. Observations from the Magnetospheric Multiscale mission Hot Plasma Composition Analyzer at the duskside magnetopause near reconnection X lines show that ions from the ring current and warm plasma cloak may Citation: Fuselier, S. A., et al. (2016), have high mass densities. However, these mass densities are not as large as the mass density in the Magnetospheric ion influence on magnetosheath. The results suggest that except for possible influence from the plasmaspheric drainage magnetic reconnection at the duskside plume, the other major magnetospheric ion populations do not greatly influence asymmetric reconnection magnetopause, Geophys.Res.Lett., 43, 1435–1442, doi:10.1002/2015GL067358. at the duskside magnetopause. Received 9 DEC 2015 1. Introduction Accepted 8 FEB 2016 Accepted article online 11 FEB 2016 Magnetic reconnection is ubiquitous at the Earth’s magnetopause for all interplanetary magnetic field (IMF) Published online 29 FEB 2016 orientations (see, e.g., recent reviews by Fuselier and Lewis [2011] and Cassak and Fuselier [2015]). Reconnection across the magnetopause is highly asymmetric because the plasma mass density in the magnetosphere is typically much lower than the mass density in the magnetosheath [e.g., Fuselier et al., 1993], and the magnetic field strength is higher in the magnetosphere. This asymmetry has important implications on the structure and rate of reconnection at the magnetopause [Cassak and Shay, 2007]. Although the magnetospheric mass density is typically low, there are times and locations at the magnetopause when this density may rival the magnetosheath mass density. At least three broadly defined ion populations may contribute significantly to the magnetospheric mass density; the magnetospheric ring current, the “warm plasma cloak”, and the plasmaspheric drainage plume. These populations are observed at times at the dusk flank magnetopause (see Figure 1) and are usually distinguishable by their energies and composition. The ring current is a medium-energy (~3–100 keV) population consisting of H+,He2+,O+,andHe+.Ionconcen- trations vary with magnetospheric activity. During relatively quiet times, H+ dominates with lower concentrations of the other ions. During active times, when magnetospheric convection is enhanced, O+ can dominate. The lower energy ring current ions (~3–30 keV) gradient drift to the duskside magnetopause as depicted schemati- cally in Figure 1. The warm plasma cloak [e.g., Chappell et al., 2008] is a lower energy (~10 eV to 3 keV) ionospheric outflow popula- tion that propagates from high latitudes into the magnetotail. The composition reflects that of ionospheric outflow: H+,O+ and, to a lesser extent, He+ [Yau et al., 1984; Collin et al., 1988]. Similar to the ring current, H+ is often dominant, but O+ can dominate ionospheric outflow during active times. The warm plasma cloak convects sunward either directly to the dawnside magnetopause or around the dawnside to thedusksidemagnetopause [e.g., Chappell et al., 2008] as depicted in Figure 1. The occurrence frequency is higher on the dawnside versus the duskside, although the density dependence at the magnetopause with local time is not known. < ©2016. American Geophysical Union. The plasmaspheric drainage plume is a low energy (typically 1 eV) ionospheric population that is an extension All Rights Reserved. of the plasmasphere on the duskside magnetosphere, as depicted in Figure 1. Its composition reflects that of FUSELIER ET AL. MAGNETOSPHERIC IONS IN RECONNECTION 1435 Geophysical Research Letters 10.1002/2015GL067358 the plasmasphere: H+,He+,and,toa lesser extent, O+. The plume and the duskside outer plasmasphere may have higher temperature (tens of eV) [e.g., Olsen et al., 1987; Labelle et al., 1988]. These magnetospheric ion populations may have high mass densities. For example, plasmaspheric material has been observed adjacent to the magne- À topause with densities >10 cm 3 [Su et al., 2000; McFadden et al., 2008; Walsh et al., 2014a, 2014b]. H+,He+, and O+ were identified in the magneto- pause boundary layers because these ion populations were cold and stream- ing with the E × B velocity in the layer [e.g., Gosling et al., 1990]. The high density and heavy ion content of these populations led to the suggestion that magnetospheric ions may modify (reduce) the reconnection rate at the magnetopause [e.g., Borovsky and Denton, 2006; Borovsky et al., 2013]. Connecting magnetospheric ion popula- tions with modification of reconnection at the magnetopause is not straightfor- ward. There are at least two complica- tionstothisconnection.Thefirst Figure 1. Schematic representation of magnetospheric plasma at the dusk- side magnetopause. Three populations, the ring current, warm plasma cloak, complication is that mass spectrometry and plasmspheric drainage plume, all convect to the duskside magneto- measurements are required to deter- pause. The grey dots show the location of eight MMS magnetopause mine the mass densities from the three crossing events. Ion composition measurements from these events are used magnetospheric ion populations. Ion to determine the effect of magnetospheric ions on magnetopause species in the plasmaspheric plume are reconnection. sometimes identifiable in the boundary layers using instrumentation that has energy analysis only. However, the plasmaspheric plume does not always remain cold [e.g., Labelle et al., 1988], necessitating mass spectrometry measurements. Furthermore, the other two populations have higher temperature and require instrumentation that resolves mass. Only a few space missions have had mass spectrometers capable of measuring all magnetospheric ion populations near the magnetopause and measurements from these missions are limited [see, e.g., Fuselier et al., 1993; Fuselier, 1995; Wang et al., 2015]. The second complication is that in situ measurements must be obtained near the magnetopause reconnec- tion X line. There is ample evidence that magnetospheric ions flow through the open magnetopause into the magnetosheath [e.g., Sonnerrup et al., 1981; Fuselier et al., 1991; Su et al., 2000]. However, simply crossing the open magnetopause does not necessarily indicate that these magnetospheric ions were near the reconnec- tion X line and therefore may have influenced the reconnection process. The purpose of this paper is to present new, mass-resolved, observations of magnetospheric and magne- tosheath mass density at the dusk flank magnetopause from the Hot Plasma Composition Analyzer (HPCA) on the Magnetospheric Multiscale (MMS) Mission [Young et al., 2014; Burch et al., 2015]. One event near the reconnection X line is discussed in detail in the next section. This discussion is followed by analysis of several other events, also near reconnection X lines. These results show that the magnetospheric mass density at the dusk flank magnetopause rarely rivals that of the magnetosheath mass density and that even in extreme instances, the effect of two of the magnetospheric ion populations on the reconnection rate is relatively small. FUSELIER ET AL.
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